1. Technical Field
This concerns signal transmission of digital signals in computing installations having rapid communication via a backplane common to a plurality of subassemblies.
2. Prior Art
Computing installations are constructed as a rule from subassemblies which exchange data with one another. These subassemblies are arranged in pluggable fashion on a carrier board and the contacts of the various plug connectors are connected to one another in each case. Hence, a multiplicity of parallel lines is produced via which in each case correspondingly many data can be transmitted during one transmission operation. Apart from these data lines, there are control lines, ground lines and power supply lines.
For the transmission, an asymmetrical drive is often used in which one data line is used per logic signal and is switched with reference to a common ground. In particular, electronic switches are used which connect a potential provided on the data line to a ground line. In the process, because of the inductances and capacitances, slow edges or even oscillations occur on the signal lines during switching on or switching off. This effect can be avoided if the signal lines are terminated with their characteristic impedance. For systems of low speed, a common plug contact for the ground connection of many signal lines is used. Since in this case, via the one or the few ground contacts, considerably higher high-frequency currents flow than via the many signal contacts, interference occurs. One known measure in high-speed applications is therefore the use of one ground contact per signal contact. This solution is ruled out if, for reasons of compatibility, a standardized contact allocation must be used in which the number of ground contacts is fixed.
In the publication DE 38 38 486 A1, a method for producing circuit substrates is specified in which signal lines are located between grounded shields.
In the publication EP 0 414 546 A2, a backplane is specified in which signal lines are arranged between layers for signal ground and voltage supply.